Paper comprises cellulose and additives. One additive is referred to as ‘ash’ and is the remaining material when the paper is burned. Paper products generally contain “ash” to enhance printability, color and other physical aspects. The most common type of additive found in paper products include Clay, Calcium Carbonate (CaCO3) and Titanium Dioxide (TiO2) but there exist other types of additives. It is well known that the weight of the paper is referred to as the Basis Weight (BW); Dry Weight (DW) is the Basis Weight minus the weight of the remaining water in the paper; and, Percentage Ash is defined as the sum of the additives divided by the Dry Weight.
Most paper qualities depend on the amount of ash content so this is tightly controlled during paper production. During production, the total ash content of a paper product or sample must be determined. X-ray absorption or X-ray fluorescence techniques are typically used to measure the individual or total concentrations of these additives.
U.S. Pat. No. 5,854,821 describes an X-ray absorption measuring system and process for measuring the three common types of paper additives. To measure ash, the '821 patent utilizes two adjacently placed x-ray sources on one side of a paper web, and two corresponding adjacent detectors placed on the opposite side of the paper web with the first source operating at an energy level higher than the of the paper web with the first source operating at an energy level higher than the second source. It is asserted that improved composition detection for ash in paper can be achieved in this manner. However, one skilled in the art will notice that operating such a system is still subject to reduced accuracy since variance of each X-ray source must also be considered.
U.S. Pat. No. 6,377,652 also describes an X-ray absorption measuring system that utilizes a “measure and calibrate” approach whereby a single X-ray source using a multiple filter/detector arrangement is used to determine the total mineral content in sheet material having at least three mineral additive components. Measurement beams are directed through a continuously advancing paper web with each beam being received by a corresponding X-ray detector on the other side of the web. Signals representative of both the beam(s) and the detector(s) are received by a computer which then compares the signals and, using well-known or readily derived equations, computes the individual component concentrations of the mineral additives in the paper web.
Those skilled in the art will notice that the signals obtained in the three detectors by such an arrangement are only slightly different and thus result in very limited accuracy of the composition.
It would be highly desirable to provide a system for implementing a technique that enables detection of the relative material composition of ash content in paper material utilizing a simple scanning X-ray sensor gauge and known fundamental physics parameters concerning the ash contents.